Topic 15 · page 17 of 28

Naming acyl chlorides and esters

Acyl chlorides end in -oyl chloride and contain –COCl. Esters are named alkyl alkanoate, with the part from the alcohol first and the part from the acid second.

12 min read15.13

Read first: Naming carboxylic acids, Esterification

One C=O part, four groups 15.13

Carboxylic acids, acyl chlorides, esters and amides are the carboxylic acid derivatives. They all contain the same acyl group, R–C=O, and differ only in what is attached to it.

Skeletal formulae of four compounds that share the same CH3C=O part: ethanoic acid with OH, ethanoyl chloride with Cl, ethyl ethanoate with O and an ethyl group, and ethanamide with NH2. The group that changes is shown in teal.
The CH₃C=O part stays the same. Only the group in teal changes.
Family Group Example Name ending
carboxylic acid –COOH CH₃COOH -oic acid
acyl chloride –COCl CH₃COCl -oyl chloride
ester –COOR CH₃COOCH₂CH₃ alkyl -oate
amide –CONH₂ CH₃CONH₂ -amide

Naming acyl chlorides 15.13

Take the name of the parent acid and change -oic acid to -oyl chloride. The carbon of the –COCl group is carbon 1, so no number is needed for it.

Acid Acyl chloride Structural formula
ethanoic acid ethanoyl chloride CH₃COCl
propanoic acid propanoyl chloride CH₃CH₂COCl
butanoic acid butanoyl chloride CH₃CH₂CH₂COCl
2-methylpropanoic acid 2-methylpropanoyl chloride (CH₃)₂CHCOCl

In a displayed formula the carbonyl carbon is bonded to the R group, to O by a double bond and to Cl. Skeletal formulae show the chain with a C=O and a Cl at one end.

Naming esters 15.13

An ester has two parts, both named:

Skeletal formulae of two esters with the parts labelled. Ethyl ethanoate: the CH3C=O part comes from ethanoic acid, giving the name ethanoate, and the O and ethyl part comes from ethanol, giving the name ethyl. Methyl propanoate: the CH3CH2C=O part comes from propanoic acid and the O and CH3 part from methanol.
The first word of the name comes from the alcohol, the second from the acid.
  1. The alkyl group attached to the oxygen comes from the alcohol. It is the first word.
  2. The acyl part (including the C=O) comes from the acid, with the ending changed to -oate. It is the second word.

So CH₃COOCH₂CH₃ is ethyl ethanoate: the –OCH₂CH₃ part is ethyl and the CH₃CO– part is ethanoate. In the formula the acid part is on the left and the alcohol part on the right. In the name the order is reversed.

Structural formula Alcohol part Acid part Name
CH₃COOCH₃ methyl ethanoate methyl ethanoate
CH₃COOCH₂CH₃ ethyl ethanoate ethyl ethanoate
CH₃CH₂COOCH₃ methyl propanoate methyl propanoate
HCOOCHX2CHX3\ce{HCOOCH2CH3} ethyl methanoate ethyl methanoate
CH₃CH₂CH₂COOCH₂CH₃ ethyl butanoate ethyl butanoate

Ethyl ethanoate and methyl propanoate both have the molecular formula C₄H₈O₂. They are isomers, and the NMR spectra later in this topic tell them apart.

Check yourself

  1. Name CH₃CH₂COCl and CH₃CH₂CH₂CH₂COCl.
  2. Name CH₃CH₂COOCH₂CH₃ and CH₃COOCH₂CH₂CH₃.
  3. Give the structural formulae of methyl butanoate and ethyl methanoate.
  4. Name the acid and the alcohol from which ethyl propanoate is made.
  5. State the molecular formula of methyl ethanoate and of ethyl methanoate, and say how they are related.

Answers cover these until you have tried the questions

  1. CH₃CH₂COCl is propanoyl chloride. CH₃CH₂CH₂CH₂COCl is pentanoyl chloride.
  2. CH₃CH₂COOCH₂CH₃ is ethyl propanoate: the alcohol part (after the O) is ethyl and the acid part is propanoate. CH₃COOCH₂CH₂CH₃ is propyl ethanoate.
  3. Methyl butanoate: CH₃CH₂CH₂COOCH₃. Ethyl methanoate: HCOOCH₂CH₃.
  4. Propanoic acid and ethanol.
  5. Both are C₃H₆O₂. They are isomers: the same atoms arranged differently, since methyl ethanoate is CH₃COOCH₃ and ethyl methanoate is HCOOCH₂CH₃.